Because Bitcoin was created in 2008 whereas gold has been a store of value for thousands of years.
People who are holding gold or taking it as an asset for so many years would really have a huge advantage out of it. Bitcoin is only new and more fresh compared to gold, because there's no digital currency present before. They really have a lot of differences and one of it is that bitcoin is much harder to earn and obtain, it is much harder to mine compared to commodity.
Gold is not stable. It's just low volatility.
This is somehow true, compared to BTC's volatility, bitcoin is much harder to make as an asset, it is much harder to control and manipulate in the market, while if you have gold, you will just hold it and you will not interfere with it because it has a lot of potential to increase more from time to time.
While BTC can be manipulated depending on the market situation if it is good to have a transaction.